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13 pages, 22076 KiB

Open AccessArticle

Cold-Sprayed AZ91D Coating and SiC/AZ91D Composite Coatings

by Yingying Wang, Bernard Normand, Xinkun Suo, Marie-Pierre Planche, Hanlin Liao and Junlei Tang

Coatings 2018, 8(4), 122; https://doi.org/10.3390/coatings8040122 - 26 Mar 2018

Cited by 10 | Viewed by 5343

Abstract

As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas [...] Read more.

As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas temperature. Compressed air was used as the accelerating gas, and although magnesium alloy is oxidation-sensitive, AZ91D coatings with good performance were obtained. The results show that dense coatings can be fabricated until the gas temperature is higher than 500 °C. The deposition efficiency increases greatly with the gas temperature, but it is lower than 10% for all coating specimens. To analyze the effects of compressed air on AZ91D powder particles and the effects of gas temperature on coatings, the phase composition, porosity, cross-sectional microstructure, and microhardness of coatings were characterized. X-ray diffraction and oxygen content analysis clarified that no phase transformation or oxidation occurred on AZ91D powder particles during cold spraying processes with compressed air. The porosity of AZ91D coatings remained between 3.6% and 3.9%. Impact melting was found on deformed AZ91D particles when the gas temperature increased to 550 °C. As-sprayed coatings exhibit much higher microhardness than as-casted bulk magnesium, demonstrating the dense structure of cold-sprayed coatings. To study the effects of ceramic particles on cold-sprayed AZ91D coatings, 15 vol % SiC powder particles were added into the feedstock powder. Lower SiC content in the coating than in the feedstock powder means that the deposition efficiency of the SiC powder particles is lower than the deposition efficiency of AZ91D particles. The addition of SiC particles reduces the porosity and increases the microhardness of cold-sprayed AZ91D coatings. The corrosion behavior of AZ91D coating and SiC reinforced AZ91D composite coating were examined. The SiC-reinforced AZ91D composite coating reveals higher corrosion potential than magnesium substrate; therefore, it serves as a cathode for the magnesium substrate, the same as the AZ91D coating on magnesium substrate. As the SiC powder is semi-conductive, the embedded SiC particles reduce the electrochemical reaction of the AZ91D coating. The addition of SiC particles increases the corrosion potential of the coating, meanwhile increasing the galvanic potential and decreasing the negative galvanic current of the coating-substrate couple. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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13 pages, 30138 KiB

Open AccessArticle

Evolution of the Three-Dimensional Structure and Growth Model of Plasma Electrolytic Oxidation Coatings on 1060 Aluminum Alloy

by Xiaohui Liu, Shuaixing Wang, Nan Du, Xinyi Li and Qing Zhao

Coatings 2018, 8(3), 105; https://doi.org/10.3390/coatings8030105 - 15 Mar 2018

Cited by 22 | Viewed by 7669

Abstract

A deeper understanding of plasma electrolytic oxidation (PEO) can in turn shed light on the evolution of coating structures during such oxidation processes. Here, a three-dimensional (3D) structure of PEO coating was investigated based on the morphologies at different locations in a PEO [...] Read more.

A deeper understanding of plasma electrolytic oxidation (PEO) can in turn shed light on the evolution of coating structures during such oxidation processes. Here, a three-dimensional (3D) structure of PEO coating was investigated based on the morphologies at different locations in a PEO coating and on the elemental distribution along certain sections. The coating surface was dominated by a crater- or pancake-like structure of alumina surrounded by Si-rich nodules. A barrier layer with a thickness of ~1 μm consisting of clustered cells was present at the aluminum/coating interface. As the coating thickened, the PEO coating gradually evolved into a distinct three-layer structure, which included a barrier layer, an internal structure with numerous closed holes, and an outer layer with a rough surface. During the PEO process, molten zones formed along with the plasma discharges. The volume and lifetime of the molten zones changed with oxidation time. The diversities of cooling rates around the molten zones resulted in structural differences along a certain section of the coating. A growth and discharge model of PEO coatings was established based on the 3D structure of the particular coating studied herein. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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14 pages, 4264 KiB

Open AccessArticle

Characterization of Electroless Ni–P Coating Prepared on a Wrought ZE10 Magnesium Alloy

by Martin Buchtík, Petr Kosár, Jaromír Wasserbauer, Jakub Tkacz and Pavel Doležal

Coatings 2018, 8(3), 96; https://doi.org/10.3390/coatings8030096 - 7 Mar 2018

Cited by 29 | Viewed by 6172

Abstract

Electroless low-phosphorus Ni–P coating was deposited on a wrought ZE10 magnesium alloy including an advanced pre-treatment of the material surface before deposition. Uniform Ni–P coating with an average thickness of 10 µm was formed by 95.6 wt % Ni and 4.4 wt % [...] Read more.

Electroless low-phosphorus Ni–P coating was deposited on a wrought ZE10 magnesium alloy including an advanced pre-treatment of the material surface before deposition. Uniform Ni–P coating with an average thickness of 10 µm was formed by 95.6 wt % Ni and 4.4 wt % P. The content of Ni and P was homogeneous in the entire cross-section of the coating. Applying the Ni–P coating to the magnesium substrate, the surface microhardness increased from 60 ± 4 HV 0.025 to 690 ± 30 HV 0.025. Using the scratch test, it was determined that deposited Ni–P coating exhibits a high degree of adhesion to the magnesium substrate. Electrochemical corrosion properties of Ni–P coating were analyzed using the polarization tests in 0.1 M NaCl, while the deposited Ni–P coating showed an improvement of the corrosion resistance when compared to the ZE10 magnesium alloy. Using the scanning electron microscopy analysis, it was determined that the fine morphology of the deposited Ni–P coating did not contain visible microcavities. The absence of macrodefects due to the adequate pre-treatment before coating was reflected on the mechanism of the coated ZE10 degradation in a 0.1 M NaCl solution. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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24128 KiB

Open AccessArticle

Particle Characterisation and Depletion of Li₂CO₃ Inhibitor in a Polyurethane Coating

by Anthony Hughes, James Laird, Chris Ryan, Peter Visser, Herman Terryn and Arjan Mol

Coatings 2017, 7(7), 106; https://doi.org/10.3390/coatings7070106 - 21 Jul 2017

Cited by 20 | Viewed by 5727

Abstract

The distribution and chemical composition of inorganic components of a corrosion-inhibiting primer based on polyurethane is determined using a range of characterisation techniques. The primer consists of a Li₂CO₃ inhibitor phase, along with other inorganic phases including TiO₂, [...] Read more.

The distribution and chemical composition of inorganic components of a corrosion-inhibiting primer based on polyurethane is determined using a range of characterisation techniques. The primer consists of a Li₂CO₃ inhibitor phase, along with other inorganic phases including TiO₂, BaSO₄ and Mg-(hydr)oxide. The characterisation techniques included particle induced X-ray and γ-ray emission spectroscopies (PIXE and PIGE, respectively) on a nuclear microprobe, as well as SEM/EDS hyperspectral mapping. Of the techniques used, only PIGE was able to directly map the Li distribution, although the distribution of Li₂CO₃ particles could be inferred from SEM through using backscatter contrast and EDS. Characterisation was also performed on a primer coating that had undergone leaching in a neutral salt spray test for 500 h. Overall, it was found that Li₂CO₃ leaching resulted in a uniform depletion zone near the surface, but also much deeper local depletion, which is thought to be due to the dissolution of clusters of Li₂CO₃ particles that were connected to the external surface/electrolyte interface. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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8830 KiB

Open AccessArticle

Corrosion Protection of Steel by Epoxy-Organoclay Nanocomposite Coatings

by Domna Merachtsaki, Panagiotis Xidas, Panagiotis Giannakoudakis, Konstantinos Triantafyllidis and Panagiotis Spathis

Coatings 2017, 7(7), 84; https://doi.org/10.3390/coatings7070084 - 22 Jun 2017

Cited by 19 | Viewed by 7091

Abstract

The purpose of the present work was to study the corrosion behavior of steel coated with epoxy-(organo) clay nanocomposite films. The investigation was carried out using salt spray exposures, optical and scanning electron microscopy examination, open circuit potential, and electrochemical impedance measurements. The [...] Read more.

The purpose of the present work was to study the corrosion behavior of steel coated with epoxy-(organo) clay nanocomposite films. The investigation was carried out using salt spray exposures, optical and scanning electron microscopy examination, open circuit potential, and electrochemical impedance measurements. The mechanical, thermomechanical, and barrier properties of pristine glassy epoxy polymer and epoxy-clay nanocomposites were examined. The degree of intercalation/exfoliation of clay nanoplatelets within the epoxy polymer also was determined. The mechanical, thermomechanical, and barrier properties of all the epoxy-clay nanocomposites were improved compared to those of the pristine epoxy polymer. In addition, both the pristine epoxy and the epoxy nanocomposite coatings protected the steel from corrosion. Furthermore, the protective properties of the nanocomposite coatings were superior compared to those of the pristine epoxy polymer. The protective properties of the nanocomposite coatings varied with the modified clay used. The epoxy-montmorillonite clay modified with primary octadecylammonium ions, Nanomer I.30E, had a better behavior than that modified with quaternary octadecylammonium ions, Nanomer I.28E. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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6571 KiB

Open AccessArticle

Preparation of Metal Coatings on Steel Balls Using Mechanical Coating Technique and Its Process Analysis

by Liang Hao, Hiroyuki Yoshida, Takaomi Itoi and Yun Lu

Coatings 2017, 7(4), 53; https://doi.org/10.3390/coatings7040053 - 10 Apr 2017

Cited by 6 | Viewed by 6109

Abstract

We successfully applied mechanical coating technique to prepare Ti coatings on the substrates of steel balls and stainless steel balls. The prepared samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The weight increase of the ball substrates and the [...] Read more.

We successfully applied mechanical coating technique to prepare Ti coatings on the substrates of steel balls and stainless steel balls. The prepared samples were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The weight increase of the ball substrates and the average thickness of Ti coatings were also monitored. The results show that continuous Ti coatings were prepared at different revolution speeds after different durations. Higher revolution speed can accelerate the formation of continuous Ti coatings. Substrate hardness also markedly affected the formation of Ti coatings. Specifically, the substance with lower surface hardness was more suitable as the substrate on which to prepare Ti coatings. The substrate material plays a key role in the formation of Ti coatings. Specifically, Ti coatings formed more easily on metal/alloy balls than ceramic balls. The above conclusion can also be applied to other metal or alloy coatings on metal/alloy and ceramic substrates. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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6604 KiB

Open AccessArticle

Internally Oxidized Ru–Zr Multilayer Coatings

by Yung-I Chen, Tso-Shen Lu and Zhi-Ting Zheng

Coatings 2017, 7(4), 46; https://doi.org/10.3390/coatings7040046 - 23 Mar 2017

Cited by 7 | Viewed by 5294

Abstract

In this study, equiatomic Ru–Zr coatings were deposited on Si wafers at 400 °C by using direct current magnetron cosputtering. The plasma focused on the circular track of the substrate holder and the substrate holder rotated at speeds within 1–30 rpm, resulting in [...] Read more.

In this study, equiatomic Ru–Zr coatings were deposited on Si wafers at 400 °C by using direct current magnetron cosputtering. The plasma focused on the circular track of the substrate holder and the substrate holder rotated at speeds within 1–30 rpm, resulting in cyclical gradient concentration in the growth direction. The nanoindentation hardness levels of the as-deposited Ru–Zr coatings increased as the stacking periods of the cyclical gradient concentration decreased. After the coatings were annealed in a 1% O₂–99% Ar atmosphere at 600 °C for 30 min, the internally oxidized coatings shifted their respective structures to a laminated structure, misaligned laminated structure, and nanocomposite, depending on their stacking periods. The effects of the stacking period of the cyclical gradient concentration on the mechanical properties and structural evolution of the annealed Ru–Zr coatings were investigated in this study. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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Review

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5939 KiB

Open AccessReview

Emerging Corrosion Inhibitors for Interfacial Coating

by Mona Taghavikish, Naba Kumar Dutta and Namita Roy Choudhury

Coatings 2017, 7(12), 217; https://doi.org/10.3390/coatings7120217 - 1 Dec 2017

Cited by 73 | Viewed by 16576

Abstract

Corrosion is a deterioration of a metal due to reaction with environment. The use of corrosion inhibitors is one of the most effective ways of protecting metal surfaces against corrosion. Their effectiveness is related to the chemical composition, their molecular structures and affinities [...] Read more.

Corrosion is a deterioration of a metal due to reaction with environment. The use of corrosion inhibitors is one of the most effective ways of protecting metal surfaces against corrosion. Their effectiveness is related to the chemical composition, their molecular structures and affinities for adsorption on the metal surface. This review focuses on the potential of ionic liquid, polyionic liquid (PIL) and graphene as promising corrosion inhibitors in emerging coatings due to their remarkable properties and various embedment or fabrication strategies. The review begins with a precise description of the synthesis, characterization and structure-property-performance relationship of such inhibitors for anti-corrosion coatings. It establishes a platform for the formation of new generation of PIL based coatings and shows that PIL corrosion inhibitors with various heteroatoms in different form can be employed for corrosion protection with higher barrier properties and protection of metal surface. However, such study is still in its infancy and there is significant scope to further develop new structures of PIL based corrosion inhibitors and coatings and study their behaviour in protection of metals. Besides, it is identified that the combination of ionic liquid, PIL and graphene could possibly contribute to the development of the ultimate corrosion inhibitor based coating. Full article

(This article belongs to the Special Issue New Generation Coatings for Metals)

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